Paint is coated on many products for improving appearance of articles. For products such as an automobile, thermosetting paints are used which cure at high temperatures of 140° C. to 250° C. for 20 minutes to 1 hour. The paints contain an isocyanate curing agent or a melamine curing agent, which is reacted with a resin included in the paints to form a cured film. However, since a high curing temperature and a long curing time needs the energy, a method of curing at a curing temperature of 100° C. to 130° C. for 20 to 40 minutes has recently been used, in view of resource saving and greenhouse gas regulation.
A curing temperature is desired to be lowered more. Film formation is required that the paint cures at such a temperature that the paint can be coated on plastic materials, for example, a temperature of 15 to 100° C., to form a cured film having high solvent resistance.
JP-A-2002-53799 (Patent Document 1) has proposed a paint for a golf ball, in which a two-pack curable urethane paint incorporating a polyol and a polyisocyanate, a curing catalyst, and a substance which forms a hydrogen bond with a hydroxy group of a polyol and volatilizes at 70° C. or lower are blended. This paint cures at low temperatures of 70° C. or lower, but needs curing for a long time (120 minutes in Example), a curing reaction is a urethane reaction, and a hydrogen bond is only used in a temporary reaction of a substance which volatilizes.
JP-T-2002-503747 (Patent Document 2) describes a method of forming powder finishing on a surface of a metal or a non-metal, in which a powder paint composition containing a resin which can be crosslinked with a functional group capable of generating a hydrogen bond (specifically, OH, COOH, NH2, NHR or SH) is applied to a substrate, and this is melted and cured by NIR (near infrared rays) irradiation. In Examples, this paint cures in a short time by irradiating near infrared rays when a polyester having a carboxy group is cured with a curing agent such as an epoxy curing agent, and it is considered that the hydrogen bond is not utilized for curing.
JP-A-6-322292 (Patent Document 3) discloses a polymer composition for hydrophilization treatment, containing a polymer (a) which is obtained by polymerizing 50 mol % or more of an unsaturated monomer having a carboxylic acid group, a polymer (b) which has a proton-accepting structural unit interacting with a carboxylic acid group with a hydrogen bonding force, and can form a polymer complex due to a hydrogen bond with the polymer (a), and a volatile base. The volatile base neutralization-reacts with a carboxylic acid group of the polymer (a) to inhibit a reaction of a polymer complex, and has volatility, and an organic amine is exemplified. In this composition, a curing temperature is 180° C. for 10 minutes in Example of Patent Document 3, and this is not low temperature curing. Additionally, the volatile base easily remains in a coated film, and becomes the cause for a coated film defect such as deteriorated water resistance, in some cases, due to possession of relatively strong interaction with carboxylic acid. Furthermore, this reaction adversely influences the environment when the volatile base has finally volatilized, in addition to limitation of utility to an aqueous system in which a neutralization reaction product can be dissolved.